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Case 1152: Anti-D Antibody in an RhD Positive Patient

Authors: Nathaniel Bigot, DO, Suzanne Bakdash, MD, MPH

Case Presentation

A pediatric patient with sickle cell disease (SCD) presented to our SCD clinic for routine follow-up and pre-transfusion testing. Cerebrovascular screening by transcranial Doppler (TCD) consistently showed elevated peak systolic flow in the middle and anterior cerebral arteries, indicating a high risk for pediatric stroke. To mitigate this risk, the patient undergoes monthly partial exchange transfusions to maintain hemoglobin S (HbS) levels below 35%. The patient types as group O RhD-positive with a negative antibody screen, though anti-Fya antibody was detected in the past. In accordance with current American Society of Hematology (ASH) guidelines concerning transfusion support for alloimmunized patients with SCD (2), red blood cell (RBC) units were selected to match the patient’s Rh (D, C/c, E/e), Kell (K), Duffy (Fya), Kidd (Jkb), and S/s phenotype. Due to these matching requirements, both group O Rh-positive and Rh-negative units were used for exchange transfusion, the most recent of which occurred one month prior to presentation. 

On current pre-transfusion testing, the patient was again typed as group O RhD-positive (Figure 1), but the antibody screen revealed a new anti-D antibody (Figure 2). The DAT (direct antiglobulin or Coombs test) was negative (Figure 3). Laboratory evaluation showed a mild drop in hemoglobin and hematocrit, together with an increase in HbS percentage. These findings fell outside the patient’s historical pre-transfusion baseline and suggested possible hemolysis with bone marrow compensation (Figure 4). The suspected hemolysis, together with the discrepancy between the blood type and newly identified anti-D antibody, prompted the blood bank to provide exclusively RhD-negative, phenotypically matched RBC units to minimize the risk of future hemolytic transfusion reactions. A blood sample was sent to a reference laboratory for RhD genotyping, which identified RHD*DAU0/DAU3.
 

Figure 1
Figure 1. Pretransfusion blood typing result using gel column agglutination testing. Anti-A, anti-B and anti-Dare mixed with patient RBCs for forward typing. A1 and B RBCs are mixed with patient plasma for reverse typing. Strong reactivity indicated by (4+), no reactivity indicated by (–). Our patient demonstrated strong (4+) reactivity on forward typing of their RBCs with anti-D typing antisera, and their blood type was interpreted as group O RhD Positive.​

 

Figure 2
Figure 2. Pretransfusion antibody screen (A) and extended antibody identification panel (B). Red circles highlight cells that agglutinated with the patient’s plasma, and the red box highlights the RhD status of the panel cells. The observed reactivity pattern is consistent with an anti-D antibody (additional rule-out cells were tested to exclude the presence of additional alloantibodies).

 

Figure 3
Figure 3. Pretransfusion direct antiglobulin test (DAT) using tube testing method. Anti-immunoglobulin added to patient's RBCs and reactivity is determined by degree of agglutination. 0 indicates no reactivity, 4+ indicates strong reactivity. Example image courtesy of Blood Bank Guy(https://www.bbguy.org/).

 

Figure 4
Figure 4.  Trends in hemoglobin (Hgb), hematocrit (Hct), and hemoglobin S (HbS) percentage over the last 10 pre-transfusion clinic visits. Each point represents a single visit, approximately one month apart, with point 10 corresponding to the most recent results. Dotted vertical red lines indicate the timing of transfusions relative to testing, which generally occurred 2 days after test results were obtained.


Diagnosis and Discussion